The United States, Britain, France, Australia and other countries are shattering records for daily reported coronavirus cases as the highly transmissible omicron upended hopes of a return to some version of normality in parts of the world.

“Right now, delta and omicron are twin threats that are driving up cases to record numbers, which again is leading to spikes in hospitalizations and deaths,” World Health Organization Director-General Tedros Adhanom Ghebreyesus, said, speaking at a press conference on Wednesday. 

“Omicron is moving so quickly,” he said, warning that he feared the variant risked causing a “tsunami of cases” that will only put increasing strain on healthcare systems around the world.  

Covid, he said, “will continue to evolve and threaten our health system if we don’t improve the collective response.”

The warning came as WHO marked two years since it was first alerted to an outbreak of an illness in Wuhan, China, that would eventually come to be known as Covid-19.

It also came as the U.S. hit a record 7-day case average of 262,034 cases on Tuesday, eclipsing a past 252,776-case record set on Jan. 11, according to an NBC News data analysis. (The data can be skewed by days with anomalous data entries, which are common around the holiday period.)

In all, 1.8 million cases were reported in the U.S. last week, however, representing a 69.3 percent increase compared to the week before.

According to the Centers for Disease Control and Prevention, omicron accounted for 58.6 percent of all Covid cases in the U.S. in the week ending on Dec. 25, while the delta variant accounted for 41.1 percent of cases.

The omicron variant appeared to make up a lower share of cases than expected, with the CDC also revising down its estimates for the week ending on Dec. 18 from 73 percent of cases being the omicron variant to 23 percent.

Meanwhile the WHO said Tuesday that the number of Covid cases recorded worldwide increased by 11 percent last week, compared with the previous week, with the biggest increase unfolding in the Americas.

The United Nations health body said there were nearly 4.99 million new cases reported around the world between Dec. 20 to Dec. 26.

However, it said that early data from Britain, South Africa and Denmark suggested there was “a reduced risk of hospitalization for the omicron compared to the delta variant,” although it stressed that further data was needed.

The U.K. also reported record numbers Tuesday, recording 129,471 new cases, the highest number of daily cases yet. The data was not complete, however, as it did not include figures for Scotland and Northern Ireland due to differences in reporting practices over the holiday period.

Despite the rise in cases, British Prime Minister Boris Johnson has said he will not introduce further coronavirus restrictions in England before the new year.

Meanwhile in Europe, France, Portugal and Greece all reported record numbers.

On Wednesday, French Health Minister Olivier Veran said the country would report 208,000 new Covid infections over the past 24 hours, breaking a record set just a day before, with 179,807 cases confirmed on Tuesday.

He said that every second around two French people have bene testing positive for Covid.

Portugal reported a record 17,172 cases on Tuesday. Government data showed that the omicron variant already represented 61.5 percent of all new cases in the country, which has one of the highest vaccination rates in the world. Around 87 percent of the population are fully jabbed.

Greece also saw its highest number of daily cases, with 21,657 new identified on Tuesday, according to the Johns Hopkins University tracker.

In Australia, Prime Minister Scott Morrison has called for a “gear change” as almost 18,300 new daily infections were recorded Tuesday, far surpassing the previous country’s previous high of around 11,300.

Morrison called a snap meeting of the national cabinet on Thursday to see what changes could be made to lessen the strain on testing laboratories and get people out of isolation faster.

“We just can’t have everybody just being taken out of circulation because they just happen to be at a particular place at a particular time,” he said in a news briefing Wednesday.

Under his plan, clinically urgent cases would be prioritized to cut down waiting times for tests and lab results, with PCR tests required only for those with symptoms.

It comes as a number of countries, including the U.S. and the U.K., have shortened isolation periods for people that test positive with Covid.

On Monday, the CDC updated its isolation guidance to allow those who have tested positive for Covid-19, but have no symptoms, to isolate for five days, down from the previous recommendation of 10 days.

Meanwhile, in the U.K., the government reduced isolation times for those with Covid, allowing those who have tested positive to exit self-isolation after seven days, instead of 10, if they have received two negative lateral flow test results.